1. Field of the Invention
The present invention relates to a power storage device and an image forming apparatus.
2. Description of the Related Art
In recent years, with increase of environmental conservation activities, there has been a growing trend in making an office environment energy-efficient. Therefore, there is a need for energy-saving in an image forming apparatus, in particular, in a type of an image forming apparatus with a heat-roller fixing device, which gives pressure and heat to a heated body such as paper and film, that requires more power.
An image forming apparatus with a heat-roller fixing device capable of high-speed image formation often uses a fixing roller that has a large heat capacity to prevent temperature of a fixing roller of a heating unit from falling in image forming operation. In this case, it takes longer time until the fixing roller reaches a temperature at which it can be used. It is undesirable that a user has to wait a long time for copying.
When an image forming apparatus enters energy-saving mode, temperature of the fixing roller is maintained lower than in standby mode. Thus, it takes long until the fixing roller reaches a usable temperature, resulting in long waiting time for a user. In other words, longer standby-mode time is preferable to reduce waiting time for a user; however, it causes consumption of more power.
To overcome the problem, some conventional image forming apparatuses have been proposed that is capable of reducing the time taken to achieve a usable temperature from energy-saving mode. For example, Japanese Patent Application Laid-open No. 2004-234996 discloses one of such conventional image forming apparatuses in which the mode is shifted from standby to energy-saving in a short time after completion of copying to reduce power consumption. The conventional image forming apparatus includes a secondary power source such as a capacitor, and supplies power from the secondary power source.
In the conventional image forming apparatus, power is supplied from a commercial alternating current (AC) power source to a fixing heater and a capacitor in a switching manner, and the capacitor as a secondary power source is charged as needed. Subsequently, power is supplied from the capacitor to the fixing heater, which is heated in a short time to a predetermined temperature. This makes it possible to reduce the time for a fixing roller to reach a usable temperature. In addition, it is possible to supply power from a commercial AC power source to both the capacitor and the fixing heater. Accordingly, a plurality of power sources is not required, leading to a simplified configuration of an image forming apparatus.
However, when power is supplied to the capacitor in the conventional image forming apparatus, a commercial power source is used for direct current (DC) power supplying and smoothed power is supplied. Thus, electric current flows into the capacitor while maintaining voltage supplied through the commercial power source. On the other hand, a capacitor is a component that is often damaged due to overcharge. To prevent it from being damaged, it is necessary to arrange an appropriate number of capacitors correspondingly to supply voltage. That is, the required number of capacitors depends on voltage supplied through a commercial power source, and therefore, a large number of capacitors are required, leading to an increase in cost. Moreover, the required number of capacitors varies according to countries because voltage supplied through a commercial power source is different in each country.